Implantable medical systems include an implantable medical device connected to an implantable medical lead. The implantable medical device is used to produce stimulation signals for delivery to tissue of a patient and/or to sense physiological signals from the tissue of the patient. The implantable medical lead includes electrical contacts on a proximal end that are connected to electrical connectors within the medical device. Electrodes are present on a distal end of the implantable medical lead to contact the tissue at the stimulation site. Filars are present within the lead to carry electrical signals between the contacts at the proximal end and the electrodes at the distal end.
The implantable medical leads can present an issue for a patient who may need to undergo a magnetic resonance imaging (MRI) scan. An MRI scan exposes the patient to radio frequency (RE) electromagnetic energy. This RF energy may be collected by the filars in the form of induced RF electrical current during the MRI scan. This RE electrical current may be delivered to the tissue of the patient via the electrodes at the distal end.
The RF electrical current induced onto the filars presents a serious condition. The electrode is a relatively small amount of surface area such that the RF electrical current from a given electrode is dissipated into a relatively small amount of tissue which may heat the tissue by an excessive amount that causes tissue damage. Furthermore, the electrode may be located adjacent to sensitive tissue such as within the brain or spine where tissue damage from the excessive heating by the induced RF current may have severe consequences.